The present invention relates to a ratchet wrench and, more particularly, to a ratchet wrench with tooth breakage resistance.
FIG. 6 of the drawings is a schematic diagram corresponding to FIG. 8 of U.S. Pat. No. 6,457,386. U.S. Pat. No. 6,457,386 discloses a ratchet wrench 2 including a driving member 23 having a chamber 231 in which a pair of first pawls 24 and a pair of second pawls 25 are mounted. A first annular gear 27 encloses one of the first pawls 24 and one of the second pawls 25. A second annular gear 27 encloses the other first pawl 24 and the other second pawl 25. A main body 21 of the ratchet wrench 2 includes a groove 212 for receiving the drive member 23 and a through-hole 211 communicating with the groove 212. Each of the first and second annular gears 27 includes a plurality of inner periphery teeth 271 and a plurality one-sided teeth 272. An inner periphery defining the groove 212 includes a plurality of inner teeth 215. First and second outer teeth 241, 241′ on the first pawls 24 and first and second outer teeth 251, 251′ on the second pawls 25 selectively engage with the inner teeth 215 of the groove 212 and the inner periphery teeth 271 of the first and second annular gears 27, prohibiting movement in a direction. The one-sided teeth 272 of the first and second annular gears 27 engage with a bevel gear 221 on an end of a drive shaft 22 to provide transmission in the reverse direction. FIG. 7 of U.S. Pat. No. 6,457,386 shows the thickness of the second pawls 25 along a rotating axis of the drive member 23 is smaller than a diameter of the through-hole 211.
When the control member 26 is pivoted, the second pawls 25 pivot to permit the first outer teeth 251 or the second outer teeth 251′ of the second pawls 25 to engage with the inner periphery teeth 271 of the first and second annular gears 27, thereby adjusting the rotating direction of the drive member 23. In the state shown in FIG. 6, the first outer teeth 241 of the first pawls 24 engage with the inner teeth 215 of the groove 212, and the first outer teeth 251 of the second pawls 25 engage with the inner periphery teeth 271 of the first and second annular gears 27. Since the one-sided teeth 272 of the first and second annular gears 27 engage with the bevel gear 22 on the drive shaft 22 to permit transmission in the reverse direction, when one of the first and second annular gears 27 rotate idly, the other of the first and second annular gears 27 drives the drive member 23 to rotate. During rotation in the reverse direction, both first and second annular gears 27 rotate idly. Thus, the drive member 23 can be driven to rotate relative to the groove 212 in either direction. Thus, a user can firstly rotate the drive shaft 22 to actuate the first and second annular gears 27 via the bevel gear 221, thereby rapidly driving the drive member 23 to tighten a fastener (not shown) to a certain extent, but not achieving the completely tightened state or a desired tightened state demanded by the user.
FIG. 7 is a diagram showing a continuing operation on the ratchet wrench in the state shown in FIG. 6. Specifically, the user operates the main body 21 to rotate the drive member 23 in the counterclockwise direction. Due to engagement between the first outer teeth 241 of the first pawls 24 and the inner teeth 215 of the groove 212 and due to the engagement between the first outer teeth 251 of the second pawls 25 and the inner periphery teeth 271 of the first and second annular gears 27 (which permits movement in a single direction), the drive member 23 rotates relative to the groove 212 and drives the fastener to the desired tightness demanded by the user. Since the thickness of the first and second pawls 25 is smaller than the diameter of the through-hole 211, one of the second pawls 25 falls into the through-hole 211 of the main body 21 and comes into contact with the end of the drive shaft 22 during the rotation of the drive member 23 relative to the groove 212.
FIG. 8 is a diagram showing a continuing operation on the ratchet wrench in the state shown in FIG. 11. Specifically, the user operates the main body 21 to rotate the drive member 23 in the clockwise direction. The first and second pawls 24 and 25 pivot relative to the drive member 23, such that the first outer teeth 241 of the first pawls 24 disengage from the inner teeth 215 of the groove 212 and such that the first outer teeth 251 of the second pawls 25 disengage from the inner periphery teeth 271 of the first and second annular gears 27. At this time, the groove 212 rotates idly relative to the drive member 23. Namely, the drive member 23 is not driven and, thus, provides a ratcheting function. After the user stops rotating the main body 21, the first outer teeth 241 of the first pawls 24 and the first outer teeth 251 of the second pawls 25 respectively reengage with the inner teeth 215 of the groove 212 and the inner periphery teeth 271 of the first and second annular gears 27 under the action of the compression springs S2 and the balls R.
When the user rapidly and repeatedly proceed with the driving rotation and the idle rotation, the drive member 23 rotates relative to the groove 212 before the drive member 23 reaches a position shown in FIG. 9. FIGS. 9 and 10 show that the first pawls 24 are pressed by the balls R biased by the compression springs S2. Before complete engagement between the inner teeth 215 of the groove 212 adjacent to the through-hole 211 (see circled portion D), only one of the first outer teeth 251 of the second pawl 25 engages with one of the inner teeth 215 in the groove 212 adjacent to the through-hole 211. Furthermore, the single-tooth engagement is not complete or is called a non-complete engagement. Namely, the contact area between these two teeth 251 and 215 shown in FIG. 10 is relatively small.
With reference to FIGS. 11 and 12, if the fastener coupled with the drive member 23 requires a large torque to reach the desired tightness demanded by the user, when the user applies a force while the first outer teeth 251 of the second pawl 25 and the inner teeth 215 in the groove 212 adjacent to the through-hole 211 have a small contact area and the non-complete engagement therebetween, a section of the one of the inner teeth 215 of groove 212 facing the through-hole 211 does not have any mechanism to withstand the force acting on the one of the outer teeth 251 of the second pawl 25. As a result, the one of the inner teeth 251 of the second pawl 25, the one of the inner teeth of the groove 212 cannot withstand the torque, leading to tooth breakage, particularly the one of the inner teeth 215 of the groove 212 adjacent to the through-hole 211.
Conclusions as a result, the user applies a force to rotate the main body 21, while the first outer teeth 251 of the second pawl 25 and the inner teeth 215 in the groove 212 adjacent to the through-hole 211 have a small contact area and the non-complete engagement therebetween. When only one of the first outer teeth 251 of the second pawl 25 non-complete engages with one of the inner teeth 215 in the groove 212 adjacent to the through-hole 211, the section of the one of the inner teeth 215 of groove 212 facing the through-hole 211 does not have any mechanism to withstand the force acting on the one of the outer teeth 251 of the second pawl 25, leading to tooth breakage.
Thus, a need exists for a novel ratchet wrench with tooth breakage resistance.